This invention relates generally to dishwashers of the household type and more particularly to tower type water distribution systems for providing a second level spray above the main dishwasher rack.
Nearly all domestic dishwasher units as made today include a lower washarm that rotates about a vertical axis. Most of the larger dishes are carried on a lower rack which rolls on wheels on ledges formed on the sides of the tub and out onto the fold down front door. An upper rack is also provided for smaller articles and cups and glasses, and it is mounted on rollers and channels near the top of the interior to also be movable in or out of the tub for loading and unloading. It has been found that a single rotary lower washarm does not always give good washability performance because the spray path can be blocked by the dishes on the lower rack and very little water may reach some articles on the upper rack. Therefore, nearly all dishwashers include an upper or second level spray mechanism to provide a spray both upward and downward beneath the upper rack to spray upward directly on the articles in that rack and downwardly onto the articles on the lower rack.
One approach has been to use a rotating washarm similar to the main or lower washarm and this upper washarm can either be mounted directly to the back of the washing machine tub which is not a structurally strong arrangement and allows the washarm and its mount to be easily damaged. An alternative arrangement is to mount the washarm directly to the upper rack and either make connection through a horizontal tube that engages a wash water supply at the back wall of the tub when the rack is held in the regular position when the door is closed, or to supply wash water to the upper rack by means of an elevating tower that rises up from the lower wash arm and makes a connection to the upper washarm.
Alternatively, the spray at this upper or intermediate level can be provided directly from the lower washarm by means of either a fixed or elevated tower mounted on the lower washarm so that wash water is supplied through the main washarm upwardly into the rotating tower and spray head. However, this suffers from the requirement of an elongated cut out in the lower rack to allow it to slide out around this tower and this central elongated cut out not only weakens the rack structurally but also takes up space and thereby reduces the capacity of the dishwasher for holding large dishes and pans.
Another approach which allows the rack to be complete except for the very center portion is to utilize a fixed tower that is mounted on the lower rack directly above the lower washarm. With this arrangement, when wash water enters the lower washarm, the arm, which is vertically moveable, moves upward by the water pressure and engages the tower mechanism and allows a portion of the water entering the lower washarm to enter the tower. By means of a driving connection, this fixed tower has a rotatable inner tower which therefore rotates with the lower washarm and provides a coordinated spray directly below the upper rack. Such an arrangement is shown in U.S. Pat. No. 4,174,723 granted Nov. 20, 1979 and assigned to the assignee of the present application. This arrangement has proved quite satisfactory, although it used a fabricated metal washarm with upper and lower inserts for engaging the rotatable tower and providing a bearing contact with the pump outlet. Such an arrangement, however, has one short coming in that any leakage, either between the washarm and the rotatable tower and between the pump outlet and the washarm decreases the amount of wash liquid available for spraying on the dishes and this reduces the general cleanability of the dishwasher. While the rotating upper tower has a rubber gasket that provides a fairly closed seal with the extension from the lower washarm, the rotating connection or seal between the lower washarm and the pump outlet has created sealing problems because of the tolerances required to eliminate any possible binding in this area.